Achieving a split/cracked wood grain effect?
There are a few ways that this can be done.

1) You could use sculpt mode to define the texture for a sculpting brush that resembles the wood patterns that you want.  Assuming default settings for version 2.7, go to the bottom panel that says "object mode" and click "sculpt mode".  In sculpt mode, expand the "Texture" tab on the left pane by clicking it and click the "New" button.  The texture will appear as a type of noise.  In the properties tab on the right, click the texture icon to get to the texture tab.  Under the texture tab, click the material icon.  You should see your brush texture.  Change the texture source from "Clouds" to "Image or Movie".  Load the image of your choice to act as a wood texture and you may begin using the brush to sculpt the mesh (if it has enough vertices).

2) Alternatively, you could use a displacement map to simulate some wood effects.  With your mesh selected, locate the object texture (go to the properties tab on the right and click the texture icon).  If the object has no textures, make a new one.  Change the texture source to "Image or Movie" and load the image you want to act as a displacement map (for these kinds of maps, the value channel is used to determine amount of displacement and so black pixels have no effect, white pixels have full effect, and everything between is interpolated).  Under the "influence" tab, check the "normal" and "displace" buttons and un-check the "color" button (unless the texture defines the color as well).  You may want to reduce the amount of displacement and tinker with it until you're satisfied.